This invention relates to a prefabricated chimney assembly of sheet metal construction and more particularly, to a dual wall chimney assembly in which only outside air is induced into the chimney flue for cooling the hot combustion gases, and further provides means for maintaining the particulate matter substantially entrained in the hot combustion gases.
Prefabricated, multi-wall chimney assemblies of sheet metal construction are known and are presently being used in dwelling constructions particularly where masonry fireplace constructions are not used. A commonly used multi-wall chimney assembly of sheet metal construction is disclosed in U.S. Pat. No. 2,634,720 which describes a thermosiphoning chimney wherein outside air is drawn down through an outer annular passage and upwardly through an inner annular passage and expelled to the outside air. The hot gases in the central flue are expelled to the atmosphere in the usual fashion. One variation of a triple wall chimney assembly is shown in U.S. Pat. No. 3,087,408, wherein air is drawn from the bottom of the chimney stack and is passed upwardly through the outer annular passages. The cooling air does not mix with the hot combustion gases in either of the above chimney designs. Another type of chimney is a dual wall chimney assembly, also of sheet metal construction, as shown in U.S. Pat. No. 2,916,983, and is a system wherein outside air is drawn in from the top through an annular passageway adjacent the flue and then conducted through an opening at its base into the flue so that the outside air rises and mixes with the hot combustion gases.
In addition, many chimney top structures are known which are adapted to be mounted on the exit end of a chimney flue of a thermosiphoning chimney such as is disclosed in U.S. Pat. Nos. 2,856,837, 3,282,194, and 4,200,038. In U.S. Pat. No. 4,200,038 a divergent nozzle mounted on the top section of the flue is used to improve the flow rate through the thermosiphoning passages of the chimney assembly and to recover the energy normally lost by the exiting flue gases. No outside air is introduced into the flue gases. In U.S. Pat. No. 615,600 two cup shaped, perforated plates, arranged complementary to each other, are mounted on a flue pipe so that ambient air is drawn through the openings in one plate and is conducted through the openings of the second plate, is inside the flue. This construction prevents the buildup of soot such as creosote. Note, however, that the openings of the plate can be closed or sealed by the user.